Commit 45e526e8 authored by Nikolay Aleksandrov's avatar Nikolay Aleksandrov Committed by David S. Miller

netconsole: fix NULL pointer dereference

We need to disable the netconsole (enabled = 0) before setting nt->np.dev
to NULL because otherwise we might still have users after the
netpoll_cleanup() since nt->enabled is set afterwards and we can
have a message which will result in a NULL pointer dereference.
It is very easy to hit dereferences all over the netpoll_send_udp function
by running the following two loops in parallel:
while [ 1 ]; do echo 1 > enabled; echo 0 > enabled; done;
while [ 1 ]; do echo 00:11:22:33:44:55 > remote_mac; done;
(the second loop is to generate messages, it can be done by anything)

We're safe to set nt->np.dev = NULL and nt->enabled = 0 with the spinlock
since it's required in the write_msg() function.
Signed-off-by: default avatarNikolay Aleksandrov <nikolay@redhat.com>
Reviewed-by: default avatarVeacelsav Falico <vfalico@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0e67d990
...@@ -310,6 +310,7 @@ static ssize_t store_enabled(struct netconsole_target *nt, ...@@ -310,6 +310,7 @@ static ssize_t store_enabled(struct netconsole_target *nt,
const char *buf, const char *buf,
size_t count) size_t count)
{ {
unsigned long flags;
int enabled; int enabled;
int err; int err;
...@@ -342,6 +343,13 @@ static ssize_t store_enabled(struct netconsole_target *nt, ...@@ -342,6 +343,13 @@ static ssize_t store_enabled(struct netconsole_target *nt,
printk(KERN_INFO "netconsole: network logging started\n"); printk(KERN_INFO "netconsole: network logging started\n");
} else { /* 0 */ } else { /* 0 */
/* We need to disable the netconsole before cleaning it up
* otherwise we might end up in write_msg() with
* nt->np.dev == NULL and nt->enabled == 1
*/
spin_lock_irqsave(&target_list_lock, flags);
nt->enabled = 0;
spin_unlock_irqrestore(&target_list_lock, flags);
netpoll_cleanup(&nt->np); netpoll_cleanup(&nt->np);
} }
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment